A wide variety of molded plastic chairs that stack one upon another are available in the marketplace. These prior art chairs have a seat, a back, front legs and rear legs directly connected to the seat, and usually have arms extending from the seat to the back. Each arm creates an opening bounded by that arm, the back and the seat. The legs extend outwardly from vertical to enable the chairs to be stacked one on top of another. In some stackable plastic chairs the rear legs of the uppermost chair extend through the openings bounded by the arms, back and seat of the chair below that chair in the stack. Stackable chairs have an advantage in that they can be stacked upon one another and placed on a pallet for easy transport. A retailer may display the stacked chairs on the same pallet on which they have been shipped. Consumers may also store several stackable chairs stacked one upon another. Plastic chairs are also advantageous because they are comfortable, inexpensive to manufacture, practical, lightweight, portable, water and weatherproof, sturdy, attractive, relatively easy to care for, and easy to move to and from a stacked arrangement.
U.S. Pat. Nos. 4,341,419 and 5,002,337 disclose examples of stackable side chairs. U.S. Pat. No. 7,401,854 discloses a stackable folding Adirondack chair. U.S. Pat. No. D688,885 discloses a stackable bar stool. All of these chairs have four legs with feet that rest on the floor or ground. For many years there has been a need for a stackable plastic rocking chair. Woodring in a series of related patents including U.S. Pat. Nos. 8,070,229, 8,313,141 and 8,960,792 discloses a monobloc rocking chair which is injection molded in one piece. He teaches that the side walls of the chair which includes the legs and the rockers must diverge outwardly from the top of the chair to the bottom so that the chairs can be stacked. Because of the outward divergence of the legs, the relatively small contact area between the floor and the rockers and the fact that the contact area changes as a person rocks in the chair, the rockers in the Woodring rocking chair can splay outwardly when a person sitting on the chair rocks back and forth. Continued rocking can cause the legs to break or cause the rockers to break away from the legs, breakage being more likely as the weight on the chair increases.
Plastic chairs for outdoor use must meet certain standard performance requirements. ASTM F 1561-03 standard sets forth specific tests to be performed in order to determine if a plastic chair meets those requirements. One test involves placing the chair on a glass surface which simulates smooth surfaces such as linoleum and wet pool decks. Three hundred pounds is placed on the chair. The chair must then hold for at least 30 minutes without failing. Failure occurs when the chair collapses or when any visible evidence of structural damage develops such as cracking. Chairs are often left up beyond 30 minutes to further evaluate performance even though that is not specified as necessary per the ASTM standard. Another test involves dropping a bag of shot onto the seat of the chair from a height of six inches above the seat. This test is conducted using a bag that weighs 150 pounds. The impact is repeated ten times. There must be no breakage or structural damage. The static load and impact tests are then repeated on plywood to simulate rougher surfaces such as textured concrete or treated lumber used on a deck. There are other tests required by the ASTM standard, but the tests described above are the core tests for that standard.
Retailers may require that other tests in addition to those outlined in the ASTM standard must be passed before they will sell a resin chair. The other tests may be derived from other standards that exist in the industry. BIFMA X5.1 requires that the chairs must pass one impact of 225 lbs. from six inches. Additional required tests may be “home-grown” where the retailer creates their own protocol such as one intended to simulate actual use. One example is a test where a rocking chair is loaded with weight such as used in a standard static load test and then rocked for a large number of cycles. Finally, there are test protocols for chairs intended to be marketed to large occupants. These chairs must withstand impacts of greater than 225 lbs.
Molded rocking chairs may be required to pass any or all of the tests described above, or other tests not described herein, to be deemed sufficient for retail distribution. It is unlikely that rocker like that illustrated in the Woodring patents will pass all of the required tests.
Consequently, there is a need for a stackable plastic rocking chair that will pass all of the tests that may be required for retail distribution.